Nowadays, the communication and information technologies are highly developed. With the emergence of the IP technology that crosses the link layer and transmission media, the application of the Internet be comes more and more popular. People require brand-new multimedia communication modes, and are no longer satisfied with the monotone voice communication mode. It is generally accepted that the IP-based mobile communication network and fixed communication network and the convergence between the Internet and the telecom network are the main development trend. To meet the increasing requirements for IP multimedia applications, the Third Generation Partnership Project (3GPP) organization introduces an IP Multimedia Subsystem (IMS) in an all-IP service network architecture on the basis of a packet bearer network. The purpose of the IMS is to provide individualized user data, screen user access modes, control the openness of service capabilities and provide multimedia communication experiences.
The IMS is a subsystem overlaid by the 3GPP R5 onto the existing PS domain of the Wideband Code Division Multiple Access (WCDMA) network. The IMS uses the PS domain as a bearer channel for its upper-layer control signaling and media transmission, and introduces the Session Initiation Protocol (SIP) as a service control protocol. By using the features of the SIP such as simplicity, scalability and convenience of combining media, the IMS provides rich multimedia services by separating service control from bearer control.
Currently, an IMS-based system provides voice services, but no better solution is available for providing multicast services.